Development of a cochlear input-impedacne measuring device and its application in the temporal bones of dogs

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Cochlear input impedance was measured in dogs by use of a newly developed ceramic divice. The device was composed of two ceramic bimorph elements, one for activation of the stapes and the other for pick-up vibration of the former element in form of an electric output, which varies corresponding to the magnitude of the cochlear impedance. Average impedance in the resected tempral bones was 2.4 Mohm at 1kHz, 2.3 Mohm at 2 kHz and 6.3 Mohm at 4 kHz, while that in live animals was 13.9 Mohm at 1kHz, 20.6 Mohm at 2kHz and 37.8 Mohm at 4kHz. Rupture of the round window caused decrease in the impedance, though with great variability in the effects. In contrast, closure of the round window by placing a dental cement caused increase in the impedance in some animals.